The goal of the present application is to determine how the protein implicated in hereditary hemochromatosis functions to regulate iron transport across epithelial cell barriers. Hereditary hemochromatosis is a disease of iron overload leading to iron accumulation in specific organs over the life time of the individual. Excess iron damages organs and results in a variety of problems such as liver failure, adult onset diabetes, heart failure, arthritus and hepatoma. It is the most common inherited disease in people of European descent affecting approximately 1 in 400 individuals. Recently the gene for this disease was identified and the protein it encodes (HFE) found to be similar to major histocompatibility class I proteins. The sequence of the molecule gives little insight into its function. Data obtained for preliminary results and previous data suggest that HFE is a negative regulator of iron uptake and mutations in the gene cause a loss of function. One model would be that HFE regulates iron transport across epithelial cell barriers by sensing the iron saturation of the iron transport protein, transferrin on the basolateral side of the cell. Iron uptake from the basolateral side via the transferrin receptor then would regulate iron transport from the apical to the basolateral side of the cell by altering intracellular iron pools. The model will be tested by measuring transferrin-meditated and transferrin- independent iron uptake in cells expressing HFE and compared to cells not expressing HFE. The long term goal of these studies is to determine how the transport of iron is regulated in the body.